For anybody who uses Redshift and has experimented with the Photographic Exposure settings in the camera, this macro attempts to replicate the same controls in comp. The math and interface design was provided by Redshift's Adrian Cruceru, who developed a similar tool for Nuke, with additional input from Saul Espinoza, who provided more tonemapping algorithms. This macro replicates the Nuke RsTonemapper gizmo to within a reasonable level of accuracy, and it also similarly matches Redshift's own render. It's not a 100% match, but it's pretty close, and most of the difference seems to be in the vignette.
Documentation and credits have been added, in addition to three more tone mapping methods: Filmic is based on John Hable's tonemap for the game Uncharted 2. Highlight Compression is a simple logarithmic squash of bright values, and Exponential Luma clamps the luminance while preserving hue.
There's still a bit of documentation to be written into it, and I may look at some efficiency improvements before submitting to Reactor, but if you'd like to have some fun with it now, here it is! Feedback is welcome.